Device for continuous extraction of alkalis from the escape gases of a cement kiln



March 31, 1970 e. DEYNAT 3,503,187

DEVICE FOR' counuuous EXTRACTION OF ALKALIS mom THE ESCAPE GASES OF A CEMENT KILN Filed Aug. 2, 1968 2 Sheets-Sheet 1 March 31, 1970 G. DEYNAT 3,50

mavxcn roxcounnuous EXTRACTION 0F ALKALIS FROM THE" ESCAPE GASES OF A CEMENT KILN Filed Aug. 2. 1968 2 Sheets-Sheet 2 FIG. 6

United States Patent O 3,503,187 DEVICE FOR CONTINUOUS EXTRACTION OF ALKALIS FROM THE ESCAPE GASES OF A CEMENT KILN Grard Deynat, Chalon-sur-Saone, France, assignor t Societe des Forges et Ateliers du Creusot, Paris, France, a company of France Filed Aug. 2, 1968, Ser. No. 749,692 Claims priority, application France, Dec. 15,1967, 132,571 Int. Cl. B01d 41/00 US. Cl. 55290 1 Claim ABSTRACT OF THE DISCLOSURE This device extracts alkali from exhaust gases of a cement kiln, includes a duct including a curtain of endless chain elements with chain cleaning arrangements for the chains.

The invention relates to a device for the continuous extraction of alkalis from the escape gases of a cement kiln, the device being more particularly adapted to be disposed in the ducting connecting the kiln to the base of the re-heating exchanger of the pulverulent materials feeding the kiln.

It is an object of the invention to provide a continuously operating extraction device which is sealed off from the outside and causes no losses of pulverulent material, and in which the removal of heat to the outside is limited to a very low value, so as to have only little effect on the thermal balance of the kiln.

According to the invention, it comprises inside the outlet ducting for the kiln gases a curtain formed by a plurality of endless resilient metal elements, preferably chains which are continuously driven and guided on return wheels outside the ducting in two opposite directions, and in each of the two return loops of the chains, the chain runs are subjected to the action of a cleaning and cooling fluid.

An exemplary embodiment of the invention will now be described in greater detail with reference to the accompanying drawings, wherein:

FIGURE 1 is a diagrammatic overall elevation of the device with its washing tanks;

FIGURE 2 is a partial section, to an enlarged scale and taken along the line IIII in FIGURE 1;

FIGURE 3 is a plan view showing a V-shaped arrangement of the curtain chain;

FIGURE 4 is a partial view showing the relative position of the chain links;

FIGURE 5 is a view corresponding to FIGURE 1, showing a variant of the duct-recovering hopper;

FIGURE 6 is an overall view similar to FIGURE 1, showing a compressed air blowing device, and

FIGURE 7 is a view corresponding to FIGURE 6, to an enlarged scale, showing a chain with sealing-tight discs.

FIGURE 1 shows the end of a kiln connected to ducting 2 for the outlet of gases to a reheater (not shown), the pulverulent materials preheated in the reheater being introduced into the kiln via channels 3. The alkali-extracting device is disposed on the ducting 2 adjacent the kiln and is mainly formed by a plurality of endless chains 4 whose two vertically oriented runs extend through the wall of the ducting 2 in guide tubes 5 attached in sealingtight relationship to the ducting.

Disposed above the ducting 2 is a frame 6 supporting wheels 7 for guiding each of the chains, one of the wheels being mounted on a shaft common to the chain assembly and driven by a motor (not shown). The two runs of each of the chains are wound on a return wheel 8 immersed in a tank 9 containing the water for washing and cooling the chains. Below the ducting 2 the chains are wound around return wheels 10 which are also immersed in a washing and cooling tank 11.

The two tanks 9, 11 have double walls to allow cooling by water circulation of the washing and cooling liquid (water) whose temperature is preferably kept at about 50-60, to accelerate the dissolving of the alkalis entrained by the chains 4, and to reduce the effect of the thermal shocks to which the chains are subjected.

The chains 4 can be disposed either in the same vertical plane, or, as shown in FIGURE 3, in two vertical planes to form two V-shaped curtains; in that case the offsetting between the adjacent chain runs can be such that the zones swept by the chains partially overlap, as shown in FIGURE 4, the chain links being also offset in height by the height of one link, from one chain run to the other.

The chains, which have oblong links, are made of a refractory steel to stand up to the elevated temperatures if the movement of the chains should cease; the links have a relatively considerable section, to avoid rapid heating as they pass through the ducting, thus enabling the speed of movement to be reduced.

In the vertical central plane of the ducting 2, the distance between the adjacent chain runs can be greater, so as to leave a passage 13 for any dust which may be at the bottom of the ducting. Between the ducting 2 and each of the tanks 9, 11, the chains can be deflected laterally, by means of wheels which are not shown, to increase the width of the tanks, and therefore the distance between the immersed chain loops. The lower tank 11, and possibly the upper tank 9, can have hoppers for recovering the dust entrained by the chains.

FIGURE 5 shows a hopper 14 associated with the lower tank 11; the chains pass over guide wheels 15 disposed in the upper portion of the hopper, and the dust is collected in the lower portion, whence it can be reintroduced into the kiln via a mechanical or pneumatic conveyor, or the bucket wheel of the kiln inlet joint.

The embodiment illustrated in FIGURE 6 differs from that illustrated in FIGURE 1, since the cleaning and cooling of the chains is performed by jets of pressurised air.

The curtain formed by the ascending and descending chain runs can be disposed as in the embodiment described hereinbefore (FIGURES 2 and 3). The loops of the chains 4 are formed on guide wheels 16 and 17, inside a casing 18 enclosing the ducting 2. The wheel 16 is driven by a motor M before passing on to the Wheels 16, 17, the chain runs are subjected to the blowing of compressed air at high pressure from nozzles 19, 20 fed respectively by fans 21,, 22. The cleaning by blowing can be completed by brushing, by means of related conjugate pairs of brushes 23, 24. The cool air supplied by the nozzles 19, 20 also cools the chain runs when they leave the ducting.

The casing 18 is attached in sealing-tight relationship to the metal envelope 2a of the ducting 2 (FIGURE 7). The chains 4 are guided through the brickwork 2b of the ducting via tubular guides 25. To ensure sealing tightness between the tubular guides and the chains, the latter have equidistant discs 26 having a diameter substantially equal to the internal diameter of the tubular guides 25.

To complete the sealing tightness and prevent entries of fresh air into the ducting, the result of which would be to reduce the thermal balance of the installation, the device can comprise two pressure detectors p and p disposed in the ducting 2 and the casing 18 respectively; a comparator 27 of the pressures p and p then controls a regulating chain whose output controls a shutter 28 disposed in an inlet duct 29 for fresh air, so that the pressure p constantly remains slightly higher than the pressure p The air introduced into the casing 18 is evacuated by a fan 30 sucking through a filter 31 a quantity of air greater than that introduced by the nozzles 19, 20; the filter 31 holds back the fine dust entrained by the suckedin air, the dust being collected by a recovery hopper 32. Larger dust, released from the chains 4 by the nozzles 19, 20 and the brushes 23, 24 is collected in a recovery hopper 33 disposed in the lower portion of the casing 18.

Of course, the extracting device with moving curtains (chains) described hereinbefore can be modified or completed by any useful accessory member without exceeding the scope of the invention. For instance, the cleaning of the moving elements of the curtain can be completed by accessory devices such as scraping, beating or shaking members; similarly, the moving curtain device can be applied to any installation requiring the continuous extraction of volatile bodies from a current of hot gases.

I claim:

1. A device for the continuous extraction of alkalis from the gases escaping from cement kilns comprising an outlet duct for the kiln gases, a curtain extending across the inside and through the wall of said outlet duct, a plurality of endless resilient metal chains forming said curtain, return wheels outside on each side of said duct, means for continuously driving said chains over said wheels in two opposite directions forming an endless loop for said curtain having spaced parallel sides within the duct, means for applying a cleaning and cooling gas to the chains, rotary brushes engaging the chains after ap- 4 plication of said gas, a casing sealed about said duct and said chains, said means for applying a cleaning and cooling gas and said rotary brushes being mounted in said casing and means for establishing a pressure in said casing lower than the pressure in said duct including a suction fan connected to said casing and a dust recovery filter interposed and connected between said casing and said fan.

References Cited UNITED STATES PATENTS 746,255 12/1903 Baggaley 55-233 1,561,758 11/1925 Wallace 261-80 1,955,277 4/1934 Fasting 55233 2,093,866 9/1937 Fasting 55 290 2,271,401 1/ 1942 Sainty 55290 2,902,834 9/1959 Bosworth et a1. 55290 3,395,518 8/1968 Krane 55-290 FOREIGN PATENTS 252,180 5/1964 Australia. 471,986 2/ 1929 Germany.

HARRY B. THORNTON, Primary Examiner B. NOZICK, Assistant Examiner US. Cl. X.R. 55291, 295, 302 

